Hi,
Although all of your supplies are exempt there will still be a requirment to register for VAT in the UK if the reverse charges go over the VAT Registration threshold.
The guidance states:
If you belong in the UK but are not already UK VAT registered and you receive supplies of B2B general rule services from overseas suppliers (that are treated as supplied where the recipient belongs), the value of those supplies must be added to the value of your own taxable supplies when determining whether you should be registered for UK VAT. Even if you make no taxable supplies yourself you may still be required to register if the value of general rule services received from overseas suppliers exceeds the registration thresholds.
Place of supply of services (VAT Notice 741A)
Thank you.